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a b s t r a c tThe three-dimensional (3D) geometry of complexly deformed regions is often beyond the scope of simple 2D and 2.5D representation in cross-sections and block diagrams. Methods must be developed for fully three-dimensional representation. A workflow for such three-dimensional modelling of structurally complex areas is presented. Data requirements are tailored to typical results of structural field work in strongly deformed rocks from mid-crustal levels. The workflow is based on data evaluation and data export using standard geographical information system and database management systems. Three-dimensional modelling in polyphase deformed areas is highly dependent on the correct interpretation of variations in the orientation of the dominant planar fabrics. The computer-aided earth-modelling software 3D GeoModeller is well adapted for managing this problem. It calculates the geometry of geological interfaces taking into account simultaneously the foliation data and location of lithological contacts. The workflow is based on iterative model refinement based on interactive editing of the geometry in section and map views with data assessment and pre-processing using GIS software. This approach assures internal consistency of the resulting three-dimensional models. Modelling of the Lower Lepontine Nappes in the Central Alps is used as an illustrative example from a complexly deformed terrain.

Structure and kinematics of the northern Simano Nappe 63 ABSTRACT New structural data allow the internal structure and kinematics of the Lower Penninic Simano Nappe to be established, together with the relationship of this unit to the underlying Leventina Gneisses and the also underlying Maggia Nappe. Three clearly distinguishable Alpine deformation phases (D1, D2, D3) are recognized within the Simano Nappe. D1 developed in mid-crustal levels under metamorphic conditions of ca. 1 GPa and 500°C and produced kilometre-scale, recumbent, north-closing anticlinal folds, called nappes. During D2 these nappes were intensely refolded on the same scale and with identical style to form the present day recumbent fold pattern. The axial planar foliation S2 is the dominant planar fabric throughout most of the Central Alps. The subsequent phase D3 overprints the entire tectonostratigraphy of the Central Alps, with broader and more upright D3 folds trending oblique to the orogen. Regionally, these broad D3 folds have a major influence on the overall foliation and nappe outcrop pattern of the Central Alps. During D2 and D3, peak metamorphic conditions reached temperatures of up to 650°C, under pressures of 0.7-0.8 GPa. An important consequence of this deformation history is that lithological units separated only by D2-synforms formed part of the same tectonostratigraphic level after D1 nappe-stacking and therefore should not be interpreted as different nappes. This principle can be directly applied to the relationship between the Simano and the two adjacent units. The underlying Leventina Gneisses are separated from the Simano rocks by an originally intrusive contact that has been strongly reactivated during both D1 and D2. Therefore, it is taken to represent a true nappe contact, although locally it still retains some original intrusive relationships and has also been strongly reactivated during D2. The Maggia and Simano units represent alternate limbs of a D2 synform-antiform pair, the Mogno synform and the Larecc antiform, or more generally the Verzasca-Larecc-Ganna antiform. If the Maggia unit is simply the continuation of the Simano unit around the D2 Mogno synform, then post-D1 they represented a single Simano-Maggia Nappe. The Maggia "Nappe" is therefore also part of the European margin and cannot be separately assigned to the Briançonnais paleogeographic domain, as has been proposed. ZUSAMMENFASSUNGNeue strukturelle Erkenntnisse erlauben es, nicht nur die interne Struktur und Kinematik der unterpenninischen Simano-Decke zu definieren, sondern auch die Beziehungen dieser Einheit mit den darunterliegenden Einheiten der Leventina-Gneise und der Maggia-Decke zu klären. Drei klar unterscheidbare alpine Deformationsphasen (D1, D2, D3) können innerhalb der SimanoDecke beobachtet werden. D1 entwickelte sich in mittelkrustalem Niveau unter Metamorphosebedingungen von etwa 1 GPa und 500 °C. Dabei wurden kilometergrosse, isoklinal nord-schliessende Antiklinalen gebildet, für welche sich die Bezeichnung "Decken" eingebürgert hat. Wä...

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